This invention relates, in general, to electrical devices having externally extending terminals, and particularly to the interconnections between such terminals and high voltage connecting members.
A well recognized problem associated with connections made between high voltage carrying members is the possibility of electrical corona discharges and/or electrical arcing caused by sharp edges or points at the connections. As known, such edges or points cause electrical charge concentrations and attendant high electrical fields. In some instances, the practice is to encase the connection joint of a device terminal with a high voltage power line within a "corona shield", i.e., a relatively large member having only smooth surfaces and well rounded corners. Disadvantages of such corona shields are that they add expense and add to the device space requirements. Indeed, in some instances, the presence of the relatively large corona shields so reduces the free space between adjacent terminals at different voltages that the risk of voltage arcing increases.
By way of example, the present invention is described in connection with a known type of electrical relay used for switching an input high voltage power line between alternate output high voltage power lines. The term "high voltage" is relative and is actually a function of the electrical device involved. Thus, even a relatively small voltage , if applied to a pointed needle, can cause voltage arcing. In the illustrative example, voltages of around 10,000 volts d.c. are switched by the relay.
In one application, for example, the illustrative relay is used in the powering of undersea telecommunication cables. During the operation of these systems, it is sometimes desirable to be able to switch power connections remotely at an undersea station. This is accomplished using a high voltage relay.
The illustrative relay is of known type comprising (FIGS. 1, 1A, 1B) an hermetically sealed envelope 10 enclosing one or more sets of relay contacts. For reducing the possibility of electrical arcing between contacts during power switching, or at other times,the envelope is either evacuated or contains a gas strongly resistant to ionization. The various relay contacts are connected, within the envelope, to terminals 12 which pass outwardly through the envelope wall 10 in hermetically sealed relation therewith. An input power line 14 is typically connected to the terminal 12, and two, or more, output power lines are connected to other terminals of the relay.
In the illustrative relay, the terminals 12 comprise solid rods of tungsten, or a glass-sealable alloy, and, as detailed in FIGS. 1 and 1B, two techniques are typically used for connecting an end 16 of each power line 14 to a respective terminal. Both techniques involve soldering or brazing the wire ends to the terminals and both techniques involve first sliding and securing a hollow tubing connector link or sleeve 18 onto the device terminals (FIG. 1B). The two techniques differ in how the wire ends are initially mechanically secured to the tubings sleeves 18.
In one technique, as illustrated in FIG. 1B, the hollow tubing 18 mounted on the terminal 12 includes a radially extending plate or tab 20 having an opening 22 therethrough. An end 16 of the power line 14 is passed through the plate opening 22 and tightly looped (typically by hand held pliers) around the plate to secure the wire end in place. The looped wire end is then soldered to the plate, taking care that the solder joint completely encapsulates the end 16 of the wire as well as most of the plate 20 in a smooth layer of solder. Provided the resulting solder layer is properly shaped and fully encloses the connection between the wire end 16 and the apertured plate 20 (as well as completely enclosing the opening 22 therethrough), associated corona discharges and electrical arcing are generally avoided, at least for limited voltage levels.
Problems, however, are that the wire wrapping and soldering processes must be quite carefully performed and, aside from being time consuming and expensive, all too often are not properly done. Moreover, even when optimally performed, the resulting joint structure is highly variable and of inherently poor shape for avoiding high electric fields. Such connections are often not adequate for cases involving close proximity to an electrical ground point. Also, corona shields are not compatible with this type of terminal design.
In another technique, illustrated in FIG. 2, the hollow tubing 18 mounted on the terminal 12 extends axially beyond the end 24 of the terminal 12. The end 16 of the power line 14 is then inserted into the hollow tubing 18 through its open end 26 and soldered in place. The resulting soldered joint can be well controlled and with good quality, but the design suffers from another major disadvantage as clarified below.
The problem is that with the specified high voltage clearance required, the axial terminal extension of FIG. 2 is not feasible in the limited physical space of many equipment designs.
As shown in FIG. 2, the end 16 of the power line 14 must be axially aligned with the tubing 18 mounted on the terminal 12. This is simply not feasible in many cases because of lack of space. In the FIG. 1 technique, for example, the power lines 14 can be routed to approach the terminals in directions transverse to the terminals and positioned inwardly from the ends 24 of the terminals 12. This means that a housing (usually at electrical ground) enclosing the relay device, and the power lines extending to and from the relay device, can have an inner diameter not much greater than the relay device and its radially extending terminals. This is not as feasible with the FIG. 2 technique because, even if the power lines are bent into directions transverse to the device terminals, the wire ends 14 must project at least a short distance radially outwardly from the tube open ends 26, and high voltage clearances to electrical ground must also be provided.
Thus, while the FIG. 2 technique is generally preferred as a high voltage design over the technique of FIG. 1, for high voltage reliability, physical space problems often prevent use of the FIG. 2 technique. For cases of higher voltage and limited space, another technique is needed. The present invention avoids the problems associated with both existing techniques, while providing improvements over both.